Evaluation of peripheral arterial disease in a patient using an oscillometric pressure signal obtained at a lower extremity of the patient

ABSTRACT

Systems, methods, and products for determining indicated blood pressure values and/or characterizing a condition of a patient. The systems, methods, and products are capable of determining indicated blood pressure values in a lower extremity of a patient using an oscillometric technique. An oscillometric signal obtained from the lower extremity of the patient is analyzed, and the patient may be classified into one of a plurality of diagnostic classes. Each diagnostic class may have an associated ratio value. Based on the diagnostic class into which the patient is classified, a selected lower extremity characteristic ratio may be selected. A lower extremity indicated blood pressure value may be obtained by oscillometric processing using the selected ratio. This lower extremity indicated blood pressure value may be used with an upper extremity indicated blood pressure value to perform an extremity blood pressure ratio (EBPR) examination.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Application No.61/385,620 filed on Sep. 23, 2010 and entitled “EVALUATION OF PERIPHERALARTERIAL DISEASE IN A PATIENT USING AN OSCILLOMETRIC PRESSURE SIGNALOBTAINED AT A LOWER EXTREMITY OF THE PATIENT”, the entirety of which isincorporated herein by reference.

BACKGROUND

Atherosclerosis of the lower extremities, also known as peripheralarterial disease (PAD), is a highly prevalent condition affecting about5% of adults over 50 years of age and about 15% of adults over 70 yearsof age in the United States. A typical symptom of PAD is pain in thelegs during exertion that is relieved with rest. However, other degreesof PAD are possible ranging from mild to severe. Patients with PAD maybe entirely asymptomatic.

One method of diagnosing PAD is to compare the blood pressure valuesfrom two patient extremities in the upper and lower limbs (e.g., leg andarm blood pressure values). This method is generally referred to hereinas an extremity blood pressure ratio (EBPR) examination. The most commonEBPR examination for the diagnosis of PAD is the ankle brachial index(ABI) examination. The ABI exam compares a blood pressure value from thebrachial artery in a patient's arm with a blood pressure value from thepatient's ankle. When the ankle and arm systolic pressure values areobtained, the ratio of ankle pressure to arm pressure is normallygreater than 1.0. An ankle/brachial ratio (ABI) that is 0.9 or less isconsidered abnormal and indicates the presence of significant PAD in thepatient. The ABI value may reflect the severity of PAD in the index limb(for example ABI values of 0.9-0.7 are consistent with mild disease, ABIvalues of 0.7-0.4 are consistent with moderate disease, and ABI valuesof less than 0.4 are consistent with severe PAD).

A variety of techniques may be used in order to determine blood pressurevalues for an EBPR procedure. For example, a sphygmomanometer (e.g., ablood pressure cuff) may be placed around an extremity of the patientand inflated to occlude blood flow through an artery. A trained healthcare provider may, for example, use a stethoscope to listen forKorotcoff sounds associated with the return of blood flow in the arteryduring deflation of the blood pressure cuff to determine systolic anddiastolic pressure within the artery. Other techniques to determineblood pressure values have been developed that may employ a Dopplerultrasound blood flow detector rather than a stethoscope to determinewhen blood flow returns to the artery (systolic pressure). However, theuse of a Doppler ultrasound blood flow detector still requires trainedhealth care providers in order to operate the detector correctly.

Another technique for determining an indicated blood pressure valueincludes obtaining a pressure signal that oscillates in a manner thatcorresponds to fluctuations in limb blood volume during deflation of ablood pressure cuff as blood flow returns to an occluded artery. Thissignal may be referred to as an oscillometric signal. The oscillometricsignal can be processed to obtain a mean arterial pressure (MAP) andindicated values of systolic and diastolic pressure. This practice hasbeen widely accepted for measurement of blood pressure in the arms ofpatients in clinical practice. However, use of the oscillometrictechnique for determining blood pressures in the lower extremities ofpatients has been questioned, particularly in cases where the patient issuffering from some degree of PAD.

SUMMARY

Against this background, it has been recognized by the presentinventor(s) that the use of oscillometric techniques may facilitate aquick determination of the presence and/or severity of PAD in a patient.The use of oscillometric techniques may be accomplished by personnellacking the skill level and special training needed for traditionalmeans of measuring blood pressure values (e.g., using a stethoscope,Doppler ultrasound blood flood detector, or the like). However, priorattempts to provide systems that utilize oscillometric techniques toarrive at lower extremity blood pressure values and/or evaluate theseverity of PAD in a patient fail to recognize the need to account forthe effects of PAD when using such oscillometric techniques. Thus, thelack of reliability of previous oscillometric techniques in determiningthe severity of PAD in a patient may be overcome using the presentinvention.

The present invention generally involves classification of a patientinto one of a plurality of diagnostic classes. The classification ofpatients into an appropriate diagnostic class may be based on anoscillometric signal in the lower extremity obtained from the patient.The classification of the patient may provide information regarding theseverity of PAD present in the patient and/or provide information forcalculating an indicated blood pressure value at a lower extremity ofthe patient based upon the diagnostic class to which the patientbelongs. “Severity of PAD” in the patient is intended to describe arange of potential severities including, for example, no PAD, mild PAD,moderate PAD, and severe PAD. As such, the use of “severity of PAD” isnot intended imply that PAD is necessarily present in the patent as, forexample, “no PAD” is a potential state encompassed by “severity of PAD.”The classification of the patient into one of the diagnostic classesallows for determination and reporting of the ABI. In turn, evaluationof a patient for PAD may be accomplished such that the evaluation ismore cost effective to conduct, accessible to more patients, andreliably administrable by less highly trained personnel. For example,the present invention may be used in large scale patient screening(e.g., at health fairs, at pharmacies, community centers, etc.).

Accordingly, a first aspect includes a method for determining anindicated blood pressure in a lower extremity of a patient. The methodincludes obtaining an oscillometric pressure signal at a location on thelower extremity. A maximum amplitude of the oscillometric pressuresignal is determined. The method further includes multiplying themaximum amplitude by a selected lower extremity characteristic ratio toobtain an adjusted amplitude within the oscillometric pressure signalcorresponding with an indicated blood pressure in the lower extremity.The selected lower extremity characteristic ratio is selected from aplurality of ratio values such that a first ratio value is selected fromthe plurality of ratio values if the patient is in a first diagnosticclass, and a second ratio value is selected from the plurality of ratiovalues if the patient is in a second diagnostic class. The firstdiagnostic class may, for example, correspond with patients havingmoderate to severe PAD, and the second diagnostic class may, forexample, correspond with patients having mild to no PAD. The method alsoincludes determining the indicated blood pressure in the lower extremityfrom the adjusted amplitude.

A second aspect includes a system operable to determine an indicatedblood pressure value at a lower extremity of a patient. The systemincludes a first pressure applicator positionable at a location on thelower extremity of a patient. The first pressure applicator iscontrollable to apply a pressure to occlude blood flow in a portion ofthe lower extremity and to reduce the pressure applied thereby to permitblood flow to return in the portion of the lower extremity. The systemalso includes a processor in operative communication with the firstpressure applicator. Additionally, the system includes a first pressuretransducer in operative communication with the first pressure applicatorto obtain a first oscillometric pressure signal from the lower extremityas pressure applied by the first pressure applicator to the lowerextremity is reduced. The first pressure transducer is also in operativecommunication with the processor. The system further includes a bloodpressure determination module executable by the processor. The bloodpressure determination module is operable to detect a maximum amplitudeof the first oscillometric pressure signal and multiply the maximumamplitude of the first oscillometric pressure signal by a selected lowerextremity characteristic ratio to provide an adjusted amplitudeassociated with the first oscillometric pressure signal to obtain anindicated blood pressure value in the lower extremity. The system alsoincludes a selection module executable by the processor. The selectionmodule is operable to select the selected lower extremity characteristicratio from a plurality of ratio values such that a first ratio value isselected from the plurality of ratio values if the patient is in a firstdiagnostic class and a second ratio value is selected from the pluralityof ratio values if the patient is in a second diagnostic class.

A third aspect includes a method of determining corresponding indicatedblood pressure values in an upper extremity and a lower extremity of apatient. The method includes determining an indicated blood pressurevalue in the upper extremity of the patient using an oscillometrictechnique. An upper extremity characteristic ratio is used indetermining the indicated blood pressure value in the upper extremityfrom an oscillometric pressure signal obtained at a location on theupper extremity. The method further includes determining an indicatedblood pressure value in the lower extremity of the patient using anoscillometric technique. A selected lower extremity characteristic ratiois used in determining the indicated blood pressure value in the lowerextremity from an oscillometric pressure signal obtained at a locationon the lower extremity. The selected lower extremity characteristicratio differs from the upper extremity characteristic ratio.Additionally, the selected lower extremity characteristic ratio isselected from a plurality of ratio values such that a first ratio valueis selected from the plurality of ratio values if the patient is in afirst diagnostic class, and a second ratio value is selected from theplurality of ratio values if the patient is in a second diagnosticclass.

A fourth aspect includes a system operable to detect one or morecharacteristics useful for characterizing a patient into a firstdiagnostic class characterized as having a first severity of peripheralarterial disease (PAD) and a second diagnostic class characterized ashaving a second severity of PAD. The system includes a first pressureapplicator positionable at a first location on a lower extremity of thepatient to occlude blood flow in a portion of the lower extremity. Thesystem also includes a processor in operative communication with thefirst pressure applicator and the second pressure applicator. The systemalso includes a first pressure transducer in operative communicationwith the first pressure applicator to obtain a first oscillometricpressure signal from the lower extremity as pressure applied by thefirst pressure applicator to the lower extremity is reduced undercontrol of the processor. The first pressure transducer is also inoperative communication with the processor. The system also includes aclassification module executable by the processor, the classificationmodule being operable to compare the first oscillometric pressure signalto a lower extremity threshold value to classify a patient into one ofthe first diagnostic class and the second diagnostic class.

A fifth aspect includes a method for detecting one or morecharacteristics useful for characterizing a patient into a firstdiagnostic class characterized as having a first severity of peripheralartery disease (PAD) and a second diagnostic class characterized ashaving a second severity of PAD. The method includes obtaining anoscillometric pressure signal at a location on a lower extremity of thepatient, determining a maximum amplitude for the oscillometric pressuresignal to provide a maximum amplitude value for the oscillometricpressure signal, and comparing the maximum amplitude value to a lowerextremity threshold value. The method also includes characterizing thepatient as being in one of the first diagnostic class and the seconddiagnostic class at least partially based on the comparing step.

A sixth aspect includes a computer program product that determines anindicated blood pressure value in a lower extremity of a patient. Thecomputer program product includes a computer readable medium havingcomputer readable program code embodied therein. The computer readableprogram code includes computer readable program code enabling aprocessor to receive an oscillometric pressure signal obtained at alocation on a lower extremity of a patient, computer readable programcode enabling a processor to determine a maximum amplitude of theoscillometric pressure signal, and computer readable program codeenabling a processor to multiply the maximum amplitude by a selectedlower extremity characteristic ratio to obtain an adjusted amplitudewithin the oscillometric pressure signal corresponding with an indicatedblood pressure in the lower extremity. The selected lower extremitycharacteristic ratio is selected from a plurality of ratio values suchthat a first ratio value is selected from the plurality of ratio valuesif the patient is in a first diagnostic class, and a second ratio valueis selected from the plurality of ratio values if the patient is in asecond diagnostic class. The computer program product also includes acomputer readable program code enabling a processor to determine theindicated blood pressure in the lower extremity from the adjustedamplitude.

A seventh aspect includes a computer program product that characterizesa condition of a patient. The computer program product includes acomputer readable medium having computer readable program code embodiedtherein. The computer readable program code includes computer readableprogram code enabling a processor to receive an oscillometric pressuresignal obtained at a location on a lower extremity of the patient,computer readable program code enabling a processor to determine amaximum amplitude of the oscillometric pressure signal to provide amaximum amplitude value of the oscillometric pressure signal, computerreadable program code enabling a processor to compare the maximumamplitude value to a lower extremity threshold value, and computerreadable program code enabling a processor to characterize the patientas being in one of a first diagnostic class and a second diagnosticclass at least partially based on the comparison of the maximumamplitude value to the lower extremity threshold value.

Refinements of the features and additional features may be applicable toany of the various aspects presented herein. The refinements andadditional features may be used individually or in any combination byany of the various aspects herein. As such, the features may be, but arenot required to be used together in any combination.

For example, in one embodiment, a transform of an oscillometric pressuresignal may be performed. The transform may be a Fourier transform, anRMS calculation, or other appropriate mathematical transform. Thetransform may be used to assist in analyzing an oscillometric signal inany of the aspects recited above. For instance, the transform mayproduce a frequency domain representation of the oscillometric pressuresignal. In one embodiment, the transform is performed on a window ofinterest of an oscillometric pressure signal (e.g., such as a portion ofthe signal surrounding a maximum amplitude of the oscillometric pressuresignal). In other embodiments, the classification of a patient into adiagnostic class may be based on comparison of the oscillometricpressure signal (such as a portion or characteristic thereof) to athreshold value or to another oscillometric pressure signal (such as anoscillometric pressure signal obtained at an upper extremity of thepatient). The diagnostic classes into which patients are classified maycorrespond to different severity of PAD in the patient.

In still other embodiments, indicated blood pressure values may be usedin an EBPR examination. For instance, an ABI may be calculated usingindicated blood pressure values. In an embodiment, various portions ofinformation (e.g., blood pressure information, classificationinformation, or other appropriate information) may be communicated to auser. For instance, information may be displayed on a display that isinterpretable by a user.

The foregoing aspects as well as other aspects and advantages will beapparent upon review of the following Detailed Description when taken inconjunction with the accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention and furtheradvantages thereof, reference is now made to the following DetailedDescription, taken in conjunction with the drawings, in which:

FIG. 1 is a schematic view of an embodiment of a system operable todetermine one or more indicated blood pressure values in variousextremities of a patient and an ABI.

FIG. 2 is a more detailed schematic view of the embodiment of the systemshown in FIG. 1 operable to determine one or more indicated bloodpressure values in various extremities of a patient and an ABI.

FIG. 3A is a graphical representation of an exemplary cuff pressurecurve and oscillometric signal useful for determining an indicated bloodpressure value in an extremity of a patient.

FIG. 3B is a graphical representation of an exemplary frequency domainrepresentation of a portion the oscillometric signal of FIG. 3A within awindow of interest defined in FIG. 3A.

FIG. 4 depicts a flowchart of an embodiment of a process for determiningone or more indicated blood pressure values in various extremities of apatient and an ABI.

FIGS. 5A-C depict a flowchart of another embodiment of a process fordetermining one or more indicated blood pressure values from anoscillometric signal.

FIG. 6 is a front view of embodiment of a device operable to determineone or more indicated blood pressure values in various extremities of apatient and an ABI.

DETAILED DESCRIPTION

FIG. 1 is a schematic view of an embodiment of a system 100 operable todetermine one or more indicated blood pressure values in a patient 150.The system 100 may include a number of pressure applicators that may bepositioned at various locations with respect to the patient 150. Thepressure applicators may be operable to occlude blood flow in thevasculature (e.g., arteries) of the patient adjacent to the pressureapplicator. In one embodiment, the pressure applicators may becontrollably inflatable blood pressure cuffs. Other pressure applicatorsmay be used that are operable to controllably occlude blood flow in thearteries of the patient and controllably release the applied pressure toallow blood flow in the arteries to return.

For instance, in one embodiment, the system may include four cuffs (110,120, 130, 140) that may be positioned with respect to the arms and legsof the patient 150 on both the right and left sides of the patient 150.In this regard, the system 100 may be operable to determine indicatedblood pressure values at each of these corresponding locations. Thelocations on the patient 150 may broadly be categorized into locationson an upper extremity or a lower extremity of the patient 150. The upperextremity of the patient generally refers to the arms, head, and uppertorso of the patient 150, while the lower extremity of the patientgenerally refers to the legs and lower body of the patient 150.

Specifically, the system 100 may include a first cuff 110 positionableon the right arm of the patient 150. The first cuff 110 may be in fluidcommunication with a control module 200 by way of first pneumatic tubing112 such that the first cuff 110 is inflatable to controllably occludethe blood flow in the portion of the right arm of the patient 150adjacent to the first cuff 110. For example, the flow of blood in thebrachial artery in the patient's right arm may be occluded by inflatingthe first cuff 110. In other embodiments, a cuff (not shown) may be inoperative communication with the control module 200 such that only datacollected by the cuff is transmitted and no fluid communication isprovided between the cuff and the control module 200. For example, thecuff itself may include a controller that controls inflation anddeflation of the cuff without being in fluid communication with thecontrol module 200. The cuff may be in operative communication with thecontrol module 200 such that data may be passed between the cuff and thecontrol module 200. For instance, the cuff and control module 200 mayinclude a wireless or wired communications channel to transmit databetween the cuff and the control module 200.

A second cuff 120 may be positionable on the left arm of the patient150. The second cuff 120 may be in fluid communication with the controlmodule 200 by way of second pneumatic tubing 122 such that the secondcuff 120 is inflatable to controllably occlude the blood flow in theportion of the left arm of the patient 150 adjacent to the second cuff120. For instance, the brachial artery in the patient's left arm may becontrollably occluded by inflating the second cuff 120. A third cuff 130may be positionable on the right leg of the patient 150 (e.g., at thepatient's ankle). The third cuff 130 may be in fluid communication withthe control module 200 by way of third pneumatic tubing 132 such thatthe third cuff 130 is inflatable to selectively occlude the blood flowin the portion of the right leg of the patient 150 adjacent to the thirdcuff 130. For example, the third cuff 130 may controllably occlude bloodflow in the dorsalis pedis or posterior tibial arteries in the right legof the patient 150 upon inflation of the third cuff 130. Further still,a fourth cuff 140 may be positionable on the left leg of the patient 150(e.g., at the left ankle of the patient 150). The fourth cuff 140 may bein fluid communication with the control module 200 by way of fourthpneumatic tubing 142 such that fourth cuff 140 is inflatable tocontrollably occlude the blood flow in the portion of the left leg ofthe patient 150 adjacent to the fourth cuff 140. For example, the bloodflow in the dorsalis pedis or posterior tibial arteries may be occludedin the left leg of the patient 150 upon inflation of the fourth cuff140.

The control module 200 may be operable to control the inflation anddeflation of each cuff (110, 120, 130, 140) individually. Thus, eachcuff (110, 120, 130, 140) may be independently used in determining anindicated blood pressure value at respective locations in the patientcorresponding to the location of the cuffs (110, 120, 130, 140). In oneembodiment, the cuffs on the right side of the patient (e.g., the firstcuff 110 and third cuff 130) may collectively be used in determining anindicated blood pressure value in the upper extremity and an indicatedblood pressure value in the lower extremity of the patient 150.Similarly, the left side cuffs (e.g., the second cuff 120 and fourthcuff 140) may collectively be used in determining an indicated bloodpressure value in the upper extremity and an indicated blood pressurevalue lower extremity of the patient 150. In any regard, indicated bloodpressure values at each location corresponding to a cuff may bedetermined.

The control module 200 is shown in greater detail in FIG. 2. Asdescribed with reference to FIG. 1, the first cuff 110 may be in fluidcommunication with the control module 200 by way of first pneumatictubing 112. Also, a first pump 216 and a first control valve 218 mayalso be in fluid communication with the first cuff 110. In this regard,the first pump 216 may be operable to inflate the first cuff 110 toocclude blood flow at the location of the first cuff 110 as describedabove. A first pressure transducer 202 may monitor the pressure in thefirst cuff 110 to prevent over pressurization of the first cuff 110during inflation. In one embodiment, a maximum upper inflation limit ofthe first cuff may be about 280 mmHg. The first control valve 218 may beoperable to control the pressure in the first cuff 110 so as to decreasethe pressure in the first cuff 110 over a period of time. In thisregard, the first control valve 218 may decrease the pressure in thefirst cuff 110 in a substantially linear manner over a desired pressurerange (e.g., between an upper inflation pressure limit and a lowerdeflation pressure limit). In other embodiments, the control valve 218may decrease the pressure in the first cuff 110 in an incremental,stepwise manner. The first pressure transducer 202 may further beoperable to monitor the pressure in the first cuff 110 during thecontrolled decrease in pressure in the first cuff 210. The instantaneouspressure in the arteries of the patient fluctuates with the heartbeat ofthe patient, which may influence the pressure in the first cuff 110 asdetected by the first pressure transducer 202. This detected fluctuatingpressure may produce a pressure signal corresponding to the measuredpressure in the first cuff 110. This pressure signal may be normalizedto compensate for the gauge pressure in the first cuff 110. Thus, aportion of the pressure signal may be removed to produce anoscillometric pressure signal associated with the location of the firstcuff 110.

The second cuff 120, the third cuff 130, and the fourth cuff 140 mayalso be operated in a manner similar to that described above with regardto the first cuff 110 to produce oscillometric signals associated withthe locations corresponding to the second cuff 120, third cuff 130, andfourth cuff 140, respectively. In this regard, the second cuff 120 maybe in operative communication with a second pump 220, a second controlvalve 222, and a second pressure transducer 204. The third cuff 130 maybe in operative communication with a third pump 224, a third controlvalve 226, and a third pressure transducer 206. The fourth cuff 140 maybe in operative communication with a fourth pump 228, a fourth controlvalve 230, and a fourth pressure transducer 208. In other embodiments,more than one cuff may be in operative communication with a single pump,a single control valve, and/or a single pressure transducer. As such,fewer pumps, control valves, and/or pressure transducers may be providedin other embodiments of a control module.

Each of the pressure transducers (202, 204, 206, 208) may be operable tomeasure a pressure signal observed in a corresponding one of the cuffs(110, 120, 130, 140). The pressure transducers (202, 204, 206, 208) maybe analog or digital transducers capable of producing analog or digitaloutputs. As shown in FIG. 2, the pressure transducers (202, 204, 206,208) may be analog pressure transducers that provide an analog outputcorresponding to the measured pressure in each cuff (110, 120, 130,140).

As discussed above, a cuff (not shown) may be provided that is operativeto communicate data to a control module. In this regard, a pump, controlvalve, and pressure transducer may be provided with the cuff at thelocation on the patient. The cuff may comprise a contained unit capableof controlling inflation and deflation of the cuff and monitoring thecuff pressure. As such, data may be transmitted (e.g., via wires orwirelessly) between the control module 200 and the cuff (e.g., thecontrol module 200 may transmit a “start” signal to begin operation ofthe cuff and the cuff may transmit pressure readings to the controlmodule 200). In this regard, the control module 200 may be a computingdevice (e.g., a laptop or desktop computer) operable to receive datafrom and/or transmit data to the cuff. Such a computing device mayexecute computer readable program code stored on a computer readablemedium (e.g. a hard drive, a flash memory, an optical drive, a floppydrive, etc.) in order to perform various processing of the data asdescribed herein.

The control module 200 may include a first filter 210 and a secondfilter 212. The first filter 210 may be in operative communication withthe first pressure transducer 202 and the second pressure transducer204. The second filter 212 may be in operative communication with thethird pressure transducer 206 and the fourth pressure transducer 208. Inother embodiments, each pressure transducer may have a separate filterto which the output of the pressure transducer is provided or differentarrangements between the pressure transducers and filters may beprovided. However, in the embodiment shown in FIG. 2, it may be thatonly one of the first and second cuffs (110, 120) are inflated at anyone time, and only one of the third and fourth cuffs (130, 140) areinflated at any one time. Thus, as discussed above, values may bedetermined for the left side and right side of the patient separately(e.g., at different instances) such that not all four cuffs (110, 120,130, 140) are inflated simultaneously.

In any regard, the filters (210, 212) may be operable to perform desiredfiltering of a received signal (e.g., high pass, low pass, and/or bandpass filtering). In the embodiment shown in FIG. 2, this may includeproviding analog filters capable of filtering analog signals.Additionally or alternatively, digital filtering may be employed toperform the desired filtering of a signal. In this regard, the filters212 and 214 may comprise hardware filters or software filters capable ofperforming the desired filtering of the received signal.

The control module 200 may also include an analog to digital (ND)converter 214. The ND converter 214 may be operable to digitize ananalog signal. The ND converter 214 may comprise multiple A/D convertersthat are provided for multiple channels corresponding to multiplepressure signal inputs received from the pressure transducers (202, 204,206, 208) by way of the filters (212, 214). In turn, the A/D converter214 may provide a digital signal to a processor 250 included in thecontrol module 200. The digital signal may include a multiplexed signalcontaining pressure signal data for each pressure transducer (202, 204,206, 208). In the case where digital pressure transducers are provided,an ND converter 214 may not be necessary.

The processor 250 may comprise one or more processors operable tocontrol various functionalities of the system 100. For example, theprocessor 250 may include one or more general purpose microprocessorscapable of executing machine readable code stored on a memory 270 inoperative communication with the processor 250. The processor 250 may,for example, include one or more application specific integratedcircuits (ASICs). The processor 250 may, for example, include one ormore field programmable gate arrays (FPGAs). Further still, acombination of the foregoing (general purpose microprocessors, ASICs,FPGAs) may be employed. In the case where multiple processors areprovided, the multiple processors may include individual processorsdedicated to specific functionalities of the system 100. For instance, aprocessor may be provided for performing mathematical transforms (e.g.,a Fourier transform) of signals as will be discussed further below.Additionally, individual processors may be provided that include videocontrol processors, interface control processors, pressure checkprocessors, or other specific functionalities provided by specificprocessors.

Further still, various modules may be provided that are executable bythe processor 250 to perform various functionalities of the system 100.For instance, in one embodiment of the system 100, a blood pressuredetermination module 272 may be provided. The blood pressuredetermination module 272 may be operable to perform various operationson an oscillometric signal to obtain an indicated blood pressure valueat least partially based on the oscillometric signal. The operationassociated with the blood pressure determination module 272 is describedin greater detail below. Additionally, a selection module 274 may beexecutable by the processor 250. The selection module 274 may beoperable to select an appropriate characteristic ratio from a pluralityof ratio values based on the classification of a patient into one of aplurality of diagnostic classes. Again, the operation associated withthe selection module 274 is described in further detail below. Also, atransform module 276 may be executable by the processor 250. Thetransform module 276 may be operable to transform an oscillometricsignal utilizing a mathematical transform. The operation associated withthe transform module 276 is described in greater detail below.Additionally, a classification module 278 may be executable by theprocessor 250. The classification module 278 may be operable to classifya patient into a diagnostic class. For instance, the classificationmodule 278 may analyze an oscillometric signal to classify a patientinto a diagnostic class. The operation of the classification module 278is described in greater detail below. These modules may be provided ashardware (e.g., ASICs, FPGAs, etc.) and/or as software in the form ofmachine readable code stored on the memory 270 and executable by theprocessor 250, as is depicted in FIG. 2.

The control module 200 may further include a removable storage interface260. The processor 250 may be in operative communication with theremovable storage interface 260 to transfer data thereto. As such, datamay be transferred between the system 100 and a removable storage medium(not shown) that may in turn be transported to and used by otherdevices.

Also, the control module 200 may include a network interface 280. Thenetwork interface 280 may be a wired or wireless interface capable ofcommunicating with a network (e.g. a wide area network, a local areanetwork, an intranet, the Internet, etc.). In this regard, the controlmodule 200 may be operable to receive data (e.g., patient data) by wayof the network interface 280 and/or transmit data (e.g., patient data)via the network interface 280.

The control module 200 may also include a display 290. The processor 250may be in operative communication with the display 290 to control thefunctionality thereof. The display 290 may be operable to displayinformation including, but not limited to, the status of the system 100,indicated blood pressure values obtained at locations of the patientcorresponding to the cuffs (110, 120, 130, 140), ratios of variousindicated blood pressure values, error messages, or other pertinentdata. The display 290 may be a touch screen display operable to alsoreceive inputs from a user. The system 100 may also include a separateinput device (not shown) operable to receive inputs from a user.

The system 100 may be operable to determine an indicated blood pressurevalue at each location at which a cuff (110, 120, 130, 140) is attached.An indicated blood pressure value for each location may be determined byperforming one or more analytical processes on an oscillometric pressuresignal obtained at each respective location by monitoring oscillationsof the pressure in the corresponding cuff as the cuff is deflated andblood flow returns to the vasculature adjacent to the cuff. While someprior systems may have employed oscillometric techniques to arrive at anindicated blood pressure value in the brachial artery of a patient, suchprior oscillometric techniques have been found to be inadequate todetermine indicated blood pressure values in the lower extremities ofpatients. A description of an oscillometric technique that overcomes theinadequacies of prior systems is presented below.

FIG. 3A depicts a graphical representation of an exemplary oscillometricsignal 320 associated with a location on an extremity of a patient. Thegraphical representation depicted in FIG. 3A may not be to scale. In thetop portion of FIG. 3A, cuff pressure curve 310 indicates the pressureover time in the cuff. In order to obtain the oscillometric signal 320shown in the bottom portion of FIG. 3A, the pressure in the cuff isgenerally raised to a level above that of the systolic blood pressure.As such, the cuff may occlude blood flow in the portion of the patientadjacent to the cuff. While the blood flow is occluded in the adjacentportion, the patient's pulsatile arterial flow causes oscillations inthe pressure 310 within the cuff. The pressure signal obtained from thecuff may be normalized to remove the portion of the signal attributableto the gauge pressure in the cuff. The result may be a normalizedoscillometric pressure signal 320. The pressure 310 within the cuff maybe incrementally lowered such that once the pressure in the vasculatureof the patient is greater than the cuff pressure 310, blood flow returnsto the vasculature of the patient adjacent to the cuff. This may resultin a change in amplitude of the oscillatory signal 320. It has beenfound that the amplitude of the oscillometric signal 320 is typically ata maximum amplitude 340 when the cuff pressure 310 is at the meanarterial pressure (MAP) 380 of the patient's vasculature adjacent to thecuff. Thus, determining the maximum amplitude 340 of the oscillometricsignal allows for correlation with the cuff pressure 310 to arrive atthe patient's MAP 380 in the location adjacent to the cuff.

In addition, a characteristic ratio may be applied to the maximumamplitude 340 of the oscillometric signal 320 to arrive at an adjustedamplitude value 360. This adjusted amplitude value 360 may be locatedwithin the oscillometric signal 320. The adjusted amplitude value 360may then be correlated to the cuff pressure 310 to arrive at anindicated blood pressure value 370. For instance, for a brachial bloodpressure measurement, standard characteristic ratios have beenestablished to produce accurate indications of systolic blood pressurevalues (e.g., a characteristic ratio of 0.50 of the MAP amplitude may beused to obtain a systolic brachial blood pressure indication). In thisregard, the adjusted amplitude value 360 may, at least in part, dependupon the characteristic ratio applied to the maximum amplitude 340.

However, characteristic ratios used for the upper extremities of apatient do not always remain accurate if used for the lower extremities.Moreover, some prior attempts to arrive at a single characteristic ratiofor determining an indicated blood pressure value at the lower extremityof patients have failed.

The system 100 shown and described above may be operable to perform aprocess whereby an oscillometric signal obtained at the lower extremityof a patient is analyzed (e.g., by a selection module and/orclassification module) and used to classify the patient into one of atleast two diagnostic classes. In the case where the oscillometric signalis associated with a lower extremity location, a different ratio valuemay be provided for each diagnostic class. Thus, an indicated bloodpressure for the lower extremity may be determined utilizing a selectedlower extremity characteristic ratio that is selected from a pluralityof ratio values at least partially based on the diagnostic class intowhich the patient is classified. Once the indicated blood pressure valuefor the lower extremity has been derived, it may be used in an EBPRexamination. For instance, an ankle-brachial pressure index (ABI) may becalculated. The ABI may be useful in determining the presence and/orseverity of PAD in a patient.

The lower extremity characteristic ratio for each diagnostic class may,for example, be empirically derived. For instance, a study was conductedwith patients whose diagnostic class was established as being in one ofa plurality of classes (e.g., patients with severe/moderate PAD in oneclass and patients with mild/no PAD in a second class). The patientswere tested using a Doppler based technique to determine blood pressurevalues at a location at the lower extremity of the patient. Anoscillometric signal was also obtained for each patient at the samelocation. Corresponding data from the Doppler based technique and theoscillometric technique were correlated and statistical methods wereemployed (e.g., a linear regression) to define a relationship betweenthe collected data. Other statistical methods (e.g., methods other thana linear regression) may have been employed to arrive at a definition ofthe relationship of the data. The data obtained via the Doppler basedtechnique and the oscillometric technique may be plotted such that theamplitude of the oscillometric signal at the Doppler systolic pressureis represented on the x-axis and the maximum amplitude of theoscillometric signal is represented on the y-axis. In this regard, abest fit line may be established on the plot such that the slope of thisbest fit line represents the best fit characteristic ratio for the data.As patients of various known diagnostic classes are tested, appropriateratio values for each diagnostic class may be determined using thistechnique. Based on the aforementioned study, for a lower extremitylocation (e.g., an ankle), a characteristic ratio within a first range(e.g., from about 0.67 to 0.73) may be employed for patients in a firstdiagnostic class (e.g., corresponding to severe/moderate PAD) and acharacteristic ratio with a second range (e.g., from about 0.56 to 0.63)may be employed for patients in a second diagnostic class (e.g.,corresponding to mild/no PAD). Based on the aforementioned study, evennarrower ranges of the lower extremity characteristic ratios may bedesirable (e.g., from about 0.69 to 0.71 for patients in the firstdiagnostic class and from about 0.57 to 0.59 for patients in the seconddiagnostic class). In this regard, a lower extremity characteristicratio of about 0.70 may, for example, be used for patients in the firstdiagnostic class (e.g., corresponding to severe/moderate PAD) and alower extremity characteristic ratio of about 0.58 may, for example, beused for patients for the second diagnostic class (e.g., correspondingto mild/no PAD). As used herein, in connection with a numerical range ora numeric value, the term “about” is intended to prevent restriction toa strict numerical range or exact numeric value. Rather, the term“about” is intended to describe insubstantial differences in numericvalues based upon the context and technology with which the term “about”is used.

Returning to FIG. 3A, when analyzing the oscillometric signals inaccordance with the foregoing, it may be useful to perform processing onthe oscillometric signal. For instance, a window of interest 390 (e.g.,surrounding the maximum amplitude 340) may be defined in theoscillometric signal 320. The data from the oscillometric signal 320within the window of interest 390 may be used to calculate amathematical transform of the oscillometric signal 320 (e.g., thetransform may produce a frequency domain representation of theoscillometric signal 320 within the window of interest 390). One exampleof such a transform 330 is shown in FIG. 3B. The transform 330 may be aFourier transform (e.g., a discrete Fourier transform or a fast Fouriertransform (FFT)). From the transform 330, various values may bedetermined that may be useful in processes that are described below. Forinstance, a maximum magnitude 332 of the transform 330 may bedetermined. The maximum magnitude 332 may occur at a fundamentalfrequency 334. These values are described below with greater detail withreference to FIGS. 4 and 5

FIG. 4 depicts a process 400 that may be performed to determine one ormore indicated blood pressure values in a patient. One or more bloodpressure cuffs (e.g., cuffs 110, 120, 130, 140 described with referenceto FIGS. 1 and 2) may be positioned (402) at various locations on apatient. For instance, in one embodiment, cuffs may be positioned (402)on at least an upper extremity and a lower extremity of the patient. Thecuffs may be inflated (404) to occlude blood flow in correspondingarteries adjacent to each of the cuffs. The cuffs may subsequently becontrollably deflated (406). During the inflation (404) and deflation(406), the pressure in each cuff may be monitored to obtain (408) anoscillometric pressure signal corresponding to the measured pressure ineach cuff as described above with reference to FIG. 3. One or more ofthe respective oscillometric signals may be processed such that variousvalues may be calculated (410) for the oscillometric signals obtained at408. For instance, a frequency and amplitude value may be calculated(410) for one or more of the oscillometric signals. With reference toFIG. 3B, the frequency may comprise the fundamental frequency 334 andthe amplitude may be derived from the maximum magnitude 332. In thisregard, the calculation (410) may also include calculating a transform(e.g., a discrete Fourier transform or an FFT) of one or more of theoscillometric signals.

The calculation (410) may be performed on a window of interest of anoscillometric signal. For instance, a window of interest may beidentified surrounding the maximum amplitude of the oscillometric signalin the time domain. In turn, the calculation (410) may involve analyzingor performing a transform on only the portion of the oscillometricsignal within the window of interest. In this regard, the calculation orprocessing requirements may be reduced and extraneous signals (e.g.,artifacts) not likely to be useful in the processing of theoscillometric signal may be ignored from the oscillometric signal.

The process 400 may also include one or more forms of signal validation.This may help to increase the probability that the oscillometric signalto be analyzed is a valid signal. For instance, the amplitude calculated(410) may be analyzed to determine (412) if the amplitude is above someminimum threshold value. A signal that does not include an amplitudethat exceeds the minimum threshold value may not be analyzable. Forinstance, the cuff from which the signal was obtained may not have beenproperly positioned on the patient or the physiology of the patient maynot have produced an analyzable signal. Additionally, the frequency ofthe oscillometric signal may be analyzed to determine (414) if thesignal has a valid frequency. The frequency of the oscillometric signalmay roughly correspond to the heart rate of the patient. Thus, frequencyvalues that are outside the bounds of a normal heart beat may indicatean oscillometric signal that is not analyzable. For instance, if thefrequency is to too high or too low, the accuracy of subsequent analysisbased on the oscillometric signal may be inaccurate. In one embodiment,the acceptable frequency range may be not less than about 40oscillations per minute and not greater than about 120 oscillations perminute. Signal validation (e.g., steps 412, 416) may be performed forone or more of the oscillometric signals that are obtained.

The process 400 may also include determining (416) if the location ofthe cuff from which the oscillometric signal was obtained is at a lowerextremity or an upper extremity of a patient. In one embodiment,dedicated cuffs may be provided for the upper extremity and the lowerextremity of the patient. Also, a user may enter information regardingthe cuff location.

In the case of an oscillometric signal obtained at an upper extremity,the process 400 may include calculating (418) an indicated bloodpressure value for the upper extremity. This may involve multiplying themaximum amplitude value of the oscillometric signal in the time domainby an upper extremity characteristic ratio to produce an adjustedamplitude value. This adjusted amplitude value may be located within theoscillometric signal and correlated to a corresponding pressure measuredin the cuff corresponding to the adjusted amplitude as shown anddescribed above with reference to FIG. 3A. The upper extremitycharacteristic ratio used to calculate (418) an indicated blood pressurevalue for an upper extremity may, in one embodiment, be about 0.52.

In the case where it is determined (416) that the oscillometric signaloriginated from a lower extremity of the patient, the process 400 mayinclude classifying (420) the patient into a diagnostic class. In oneembodiment, two diagnostic classes may be established into whichpatients may be classified (420). The classification (420) of a patientinto a diagnostic class may be based upon calculated values from theoscillometric signal obtained at the lower extremity. For instance, ifthe amplitude of the oscillometric signal (e.g., as determined from themagnitude at the fundamental frequency of an FFT of the portion of theoscillometric pressure signal within a window of interest) at the lowerextremity is below a certain threshold, the patient may be classified(420) into a first diagnostic class, whereas if the maximum amplitude ofthe oscillometric signal at the lower extremity is above a certainthreshold, the patient may be classified (420) into a second diagnosticclass. The threshold value used to classify patients may be a fixedvalue (e.g., an empirically derived value) or based upon anothermeasured or calculated value. For instance, the threshold value used inthe classification (420) may, in one embodiment, be based upon theamplitude of an oscillometric signal obtained at an upper extremity ofthe patient. In this regard, the patient may be classified into adiagnostic class based on whether the amplitude of the oscillometricsignal obtained at the lower extremity is less than or greater than acertain percentage of the amplitude of the oscillometric signal obtainedat the upper extremity.

The process 400 may also include selection (422) of a selected lowerextremity characteristic ratio from a plurality of ratio values for usein the calculation (424) of an indicated blood pressure value at thelower extremity. The selection (422) may be based upon theclassification (420) of the patient into a diagnostic class. As anexample, each diagnostic class may be correlated with a correspondingratio value. Thus, the selection (422) may depend on the diagnosticclass into which the patient is classified (420). The diagnostic classesmay be based upon an indication of moderate to severe PAD in the patientfor the first diagnostic class and an indication of mild to no PAD inthe patient for the second diagnostic class.

In one embodiment, the first diagnostic class, corresponding to the casewhere the amplitude of the oscillometric signal obtained at the lowerextremity falls below a threshold value, may have a corresponding ratiovalue not less than about 0.67 and not greater than about 0.73. Forinstance, the ratio value of the first diagnostic class may be in therange of about 0.69 to 0.71. In one embodiment, the ratio value for thefirst diagnostic class is about 0.70. The second diagnostic class,corresponding to the case where the amplitude of the oscillometricsignal obtained at the lower extremity exceeds the threshold value, mayhave a corresponding ratio value not less than about 0.56 and notgreater than about 0.63. For instance, the ratio value of the seconddiagnostic class may be in the range of about 0.57 to 0.59. In oneembodiment, the ratio value for the second diagnostic class is about0.58. In turn, after the selection (422) of a selected lower extremitycharacteristic ratio, the selected ratio may be used to calculate (426)an indicated blood pressure value at the lower extremity in a process asdescribed above with respect to FIG. 3, wherein the characteristic ratioused is the selected lower extremity characteristic ratio.

In one embodiment, the indicated blood pressure value calculated (418)for the upper extremity and the indicated blood pressure valuecalculated (424) for the lower extremity may be used to furthercalculate (426) an EBPR. The EBPR may subsequently be displayed (428) orcommunicated to a user. In one embodiment, the lower extremity cuff maybe located adjacent to an ankle of the patient such that the indicatedblood pressure value for the lower extremity is obtained at the ankle.The upper extremity cuff may be located on an upper portion of the armof the patient such that the indicated blood pressure value for theupper extremity is obtained for the brachial artery in the patient'sarm. Thus, the calculation (426) may produce an ankle-brachial pressureindex (ABI) that may in turn be used to evaluate the presence and/orseverity of PAD in the patient.

In another embodiment, the process 400 shown in FIG. 4 may not involvecalculation of quantitative indicated blood pressure values or bloodpressure ratios. For instance, the classification (420) of the patientinto a diagnostic class may provide information regarding the presenceand/or severity of PAD in the patient. As stated above, classificationinto the first diagnostic class may be an indication of moderate tosevere PAD in the patient. Thus, even if a quantitative value for anindicated blood pressure value or blood pressure ratio is notdetermined, the process 400 may involve indicating the class into whichthe patient is classified or an indication that the patient may besuffering from PAD and/or the severity of PAD in the patient. Thisinformation alone may be valuable to a user when trying to determine ifand/or to what severity the patient is suffering from PAD. For instance,an indication that mild to no PAD may be presented to a user if thepatient is classified (420) into the second diagnostic class and anindication of moderate to severe PAD may be presented to a user if thepatient is classified (420) into the second diagnostic class regardlessof whether quantitative values of indicated blood pressure or ABI arecalculated.

Another example of a process 500 for determining one or more indicatedblood pressure values, an ABI, or an indication as to the presenceand/or severity of PAD in a patient is shown in FIGS. 5A-C. Thefollowing discussion of FIGS. 5A-C may reference certain variables usedin the process 500. These variables may be measured or calculated. Forexample, as shown and described with reference to FIG. 3B, a Fouriertransform (e.g., an FFT) may be applied to an oscillometric signal todetermine one or more of the variables shown and described withreference to FIGS. 5A-C. With further reference to FIGS. 3A and 3B, inone embodiment, a window of interest 390 of an oscillometric pressuresignal may be analyzed to arrive at the variables used in the process500. Variables corresponding to the upper extremity oscillometric signalmay be designated with the subscript “arm,” while variablescorresponding to the lower extremity oscillometric signal may bedesignated with the subscript “ank.” The value FFTamp may represent anamplitude (e.g., a maximum amplitude) at the fundamental frequency 334of the oscillometric signal within a window of interest as determinedfrom an FFT of the oscillometric signal. The value of FFTamp may becalculated from the maximum magnitude value 332 shown in FIG. 3B. In oneembodiment, known techniques may be used to calculate the amplitude atthe fundamental frequency from the maximum magnitude value 332. Theamplitude at the fundamental frequency may correspond with the valueFFTamp as used in the process 500. The value FFTfreq may represent thefundamental frequency 334 of the oscillometric signal within the windowof interest 390 as determined from the FFT 330 of the oscillometricsignal. The value OSCfreq may be the frequency of the oscillometricsignal as determined by a peak detection technique in the time domain(e.g., represented as the oscillometric signal 320 with reference toFIG. 3A). The variable PRESup may correspond to a detected conditionwherein the upper inflation pressure limit of the cuff was notsufficient to determine an indicated blood pressure. The variablePRESdown may correspond to a detected condition wherein the lowerdeflation pressure limit of the cuff was not sufficient to obtain anindicated blood pressure. One or more of the frequency variables may becalculated (e.g., during the calculation step 410 of the method depictedin FIG. 4).

Turning to FIG. 5A, the FFTamp value (e.g., derived from theoscillometric signal) may be analyzed to determine (502) if it is abovea minimum threshold value. The minimum threshold value may represent theminimum amplitude required to achieve an accurate result. Furthermore,an FFTamp value below the minimum threshold value may be indicative ofan incorrectly installed cuff or a patient whose physiology is such thatthe signal obtained at a cuff cannot be analyzed.

If the value for FFTamp is less than the minimum threshold value, theprocess 500 may terminate and an indication that the oscillometricsignal is not analyzable may be displayed (504). Alternatively, if theFFTamp value of the oscillometric signal is above the minimum thresholdvalue, the process may include determining (506) if a PRESdown conditionwas detected. As described above, the cuff may be controllably deflatedthrough a pressure range between an upper inflation pressure limit and alower deflation pressure limit. The PRESdown condition may be triggeredwhen the lower deflation pressure limit to which the cuff is deflated isnot sufficiently low to allow unobstructed flow of blood in the arteriesadjacent to the cuff. The PRESdown condition may be detected when theoscillometric signal indicates a maximum amplitude of the signal has notyet been reached when the cuff is deflated to the lower deflationpressure limit.

If the PRESdown condition is not detected (506), the process 500 mayproceed. If the PRESdown condition is detected (506), it may bedetermined (508) if the lower deflation pressure limit is set above aminimum value. For instance, in one embodiment, the minimum value of thelower deflation pressure limit is about 40 mmHg. If the lower deflationpressure limit is set above the minimum value, the deflation pressurelimit is reduced (510) and the process 500 may be restarted with thelower deflation pressure limit reduced. If, on the other hand, the lowerdeflation pressure limit is at the minimum lower deflation pressurelimit, the process 500 may end and an indication that the oscillometricsignal is not analyzable may be displayed (504).

The process 500 may also include a determination (510) of whether theoscillometric signal being analyzed is obtained at a lower extremity oran upper extremity. As stated above, dedicated cuffs may be used toobtain upper and lower extremity measurements, and/or a user may beprompted to input the location of a given cuff.

In the case where the oscillometric signal being analyzed was obtainedat an upper extremity, it may be determined (512) if the value forFFTamp(arm) is below an upper extremity threshold value specific tosignals obtained at an upper extremity. The upper extremity thresholdvalue may be a value for the amplitude of the oscillometric signal thatis greater than the minimum threshold used at 502. If the FFTamp(arm)value is below the upper extremity threshold value, the process 500 mayterminate and an indication that the oscillometric signal is notanalyzable may be displayed (504). Again, an FFTamp(arm) value below theupper extremity threshold value may indicate that the signal in notanalyzable (e.g., due to the physiology of the patient, an artifact inthe signal, or an error). If, however, the value for FFTamp(arm) isabove the upper extremity threshold value, the process 500 may proceedto determine (514) if a PRESup condition is detected. The PRESupcondition corresponds to a case where an upper inflation pressure limitof a cuff was not sufficient to fully occlude the flow of blood in oneor more arteries adjacent to the cuff. The PRESup condition may bedetected when the adjusted amplitude (e.g., obtained by applying anappropriate characteristic ratio to a maximum amplitude) cannot belocated in the oscillometric signal.

If a PRESup condition is detected, it is determined (516) if the upperinflation pressure limit is set below a maximum value for the upperinflation pressure limit. In one embodiment, the maximum value for theupper inflation pressure limit may be about 280 mmHg. If the upperinflation pressure limit is set at the maximum value, the process 500may terminate and an indication that the oscillometric signal is notanalyzable may be displayed (504). In contrast, if available, the upperinflation pressure limit is increased (518) and the process 500 mayrestart. If, at 514, it is determined that a PRESup condition was notdetected, the process 500 may proceed to step 527 shown in FIG. 3B,which is described in more detail below.

In the case where it is determined (511) that the oscillometric signalis obtained at a lower extremity of the patient, the process 500 mayinclude analyzing the oscillometric signal to determine (520) if thevalue for FFTamp(ank) is below a lower extremity threshold value. Thelower extremity threshold value may be greater than the minimumthreshold used at 502 and greater than the upper extremity thresholdvalue used at 512. This determination (520) of whether the value ofFFTamp(ank) is above or below the lower extremity threshold value mayprovide an indication of the presence and/or severity of PAD in thepatient. An FFTamp(ank) value below the threshold value may indicate thepatient belongs to a first diagnostic class (e.g., an FFTamp(ank) valuebelow the lower extremity threshold may indicate moderate to severe PADin the patient). In contrast, an FFTamp(ank) value above the thresholdvalue may indicate the patient belongs to a second diagnostic class(e.g., an FFTamp(ank) value above the lower extremity threshold mayindicate mild or no PAD in the patient). As described above withreference to FIG. 4, an indication as to the severity of PAD in apatient may be presented based upon the determination (520) into whichdiagnostic class the patient belongs. In this regard, even if aquantitative value of an indicated blood pressure value is notdetermined, the process 500 may include indicating to a user thediagnostic class to which the patient belongs. This information may bevaluable to a user in determining the severity of PAD in the patient.

The lower extremity threshold value may be empirically derived based onan analysis of patients known to be suffering from PAD and patientsknown to be not suffering from PAD. In other embodiments, the lowerextremity threshold value may be variable and determined by othermeasurements or calculations in the process 500. For instance, the lowerextremity threshold value may be at least partially based on an analysisof an oscillometric pressure signal obtained at an upper extremity ofthe same patient. Regardless of how the lower extremity threshold valueis derived or determined, the patient may be classified into a firstdiagnostic class 522 (characterized in FIG. 5A as Phase1=1) or a seconddiagnostic class 524 (characterized in FIG. 5A as Phase1=0) based uponwhether the value of FFTamp(ank) is above or below the lower extremitythreshold value. In any regard, the process may continue to step 527,shown in FIG. 5B.

Turning to FIG. 5B, the oscillometric signal may be analyzed todetermine (527) if the oscillometric signal has a valid frequency value.The FFTfreq value (e.g., as determined using an FFT 330 of anoscillometric signal as shown with respect to FIG. 3B) may correspondwith the heartbeat of the patient. Additionally, a range of values ofvalid frequencies may be provided for the FFTfreq value that roughlycorrespond to a normal range of patient heart rates. For example, therange of acceptable values for FFTfreq may be not less than about 43oscillations (beats) per minute and not greater than about 120oscillations (beats) per minute. If the FFTfreq value falls outside ofthis acceptable range, the process 500 may terminate and an indicationthat the oscillometric signal is not analyzable may be displayed (504).On the other hand, if the FFTfreq value is within the valid range, theprocess 500 may continue and it may be determined (528) if theoscillometric signal is obtained at a lower extremity.

In the case where the oscillometric signal is obtained at an upperextremity of the patient, the FFTfreq(arm) value may be stored (530) forfuture reference in the process as will be described further below.Furthermore, the indicated blood pressure value in the upper extremitymay be calculated (532). The calculation (532) of the indicated bloodpressure value in the upper extremity may use an upper extremitycharacteristic ratio to arrive at the indicated blood pressure value inthe upper extremity. This upper extremity characteristic ratio maycomprise a traditional characteristic ratio known in the art that isused to determine brachial indicted blood pressure values in anoscillometric process. As such, the upper extremity characteristic ratiomay be about 0.52.

If, in contrast, it is determined (528) that the oscillometric signal isderived from a lower extremity of the patient, the process 500 mayinvolve determining (534) if the FFTfreq(ank) value (e.g., thefundamental frequency of the signal) is equal to the OSCfreq(ank) value(e.g., the frequency of the signal using peak detection in the timedomain). As stated above, the OSCfreq(ank) value may be derived using atechnique applied to the oscillometric signal different from thetechnique applied to the oscillometric signal used to determineFFTfreq(ank). In this regard, the determining (534) may provideadditional means of signal validation. For example, if the two valuesare not equal, it may indicate some signal corruption (e.g., due to anartifact, noise, etc.). If the two values are within plus or minus aspecified number of oscillations (beats) per minute (e.g., +/−15 beatsper minute), the two values may be determined to be equal and theprocess 500 may proceed to step 542 shown in FIG. 5C, which is describedin more detail below.

If the FFTfreq(ank) and OSCfreq(ank) values are not equal, and it isdetermined (538) that the patient was classified into the firstdiagnostic class 522, the process 500 may terminate and an indicationthat the oscillometric signal is not analyzable may be displayed (504).This may be because the oscillometric pressure signal derived from apatient may not have characteristics sufficient to continue the process500 to arrive at reliable results. Moreover, the classification of thepatient into the first diagnostic class 522 may provide a reliableindication as to the presence and/or severity of PAD in the patient.Thus, as described above, an indication as to the presence and/orseverity of PAD in the patient or an indication of abnormal results maybe displayed without quantitative values. If, instead the patient is notin the first diagnostic class 522, the OSCfreq(ank) value may beindicated (540) as being out of range. The indication (540) thatOSCfreq(ank) is out of range may be used elsewhere in the process 500.In any regard, the process may proceed to step 542 shown in FIG. 5C. Theprocess 500 may continue in the case of the patient being classifiedinto the second diagnostic class 524 because the derived signal may havecharacteristics that are more likely to produce reliable results.

Turning to FIG. 5C, it may be determined (542) if a valid value forFFTfreq(arm) has been stored at 530 in FIG. 5B. If no FFTfreq(arm) valuehas been stored, it may be determined (544) if the patient has beenclassified into the first diagnostic class 522. If the patient is in thefirst diagnostic class 522, the process may be suspended (546) until anFFTfreq(arm) value is later determined (e.g., on a subsequent cycle ofone of the upper extremity cuffs). If the patient is not in the firstdiagnostic class 522, the process 500 may continue to step 552 which isdescribed in greater detail below.

If it is determined (542) that an FFTfreq(arm) value has been stored,the process 500 may proceed with a determination (548) as to whether theFFTfreq(ank) value is equal to the FFTfreq(arm) value that was stored.The comparison of these frequency values for the upper extremity and thelower extremity may provide an indication as to whether the cuffs arecorrectly positioned on a patient or whether an error has occurred. Asthe FFTfreq(arm) and FFTfreq(ank) values may both be dependent upon theheart rate of the patient, these two values are likely not to besignificantly different for a normal patient where the cuffs arecorrectly placed. In the instance that these values are significantlydifferent (e.g., more than +/−15 oscillations per minute apart), it maybe that the cuffs are not correctly positioned or not positioned on thepatient at all. However, if the values are within, for example, +/−15oscillations per minute, the signals may be deemed to be equal. If thevalues of FFTfreq(ank) and FFTfreq(arm) are not equal, the process 500may terminate and an indication that the oscillometric signal is notanalyzable may be displayed (504). In contrast, if the values are equal,it may be determined (550) into which diagnostic class the patient isclassified for the purpose of selecting an appropriate selected lowerextremity characteristic ratio that may in turn be used to determine anindicated blood pressure value.

If the patient is in the second diagnostic class 524 as described ateither of steps 544 or 550, the process 500 may include determining(552) if a PRESup condition is detected. If the PRESup condition is notdetected, the characteristic ratio for the second diagnostic class maybe selected and an indicated blood pressure value may be calculated(554) using the selected lower extremity characterization ratio (e.g.,of about 0.58 for the second diagnostic class). If a PRESup condition isdetected, it may be determined (556) if the upper inflation pressurelimit for the cuff is set to the maximum value for the upper inflationpressure limit. If the upper inflation pressure limit is set to themaximum value, the process 500 may terminate and an indication that theoscillometric signal is not analyzable may be displayed (504). If theupper inflation pressure limit is not set to the maximum value, theupper inflation pressure limit may be increased (558) and the processmay restart.

If it is determined (550) that the patient is in the first diagnosticclass 522, it may be determined (560) if the OSCfreq(ank) value is outof range as determined at 540 with reference to FIG. 5B. If the valuefor OSCfreq(ank) is out of range, the process 500 may include indicating(562) the process resulted in an abnormal result. This may be anindication that in the patient is likely suffering from PAD. Theindication (562) that the patient is likely suffering from PAD may notinclude a quantitative indicated blood pressure value for the lowerextremity, but rather may indicate, based on the oscillometric signalanalysis, an abnormal result may provide some indication as to theseverity of PAD in the patient.

If, on the other hand, the value for OSCfreq(ank) is not out of range,it may be determined (564) if a PRESup condition is detected. If aPRESup condition is detected, the process 500 may include indicating(562) the severity of PAD in the patient. Again, the indication (562)may not include a quantitative value for an indicated blood pressurevalue in the lower extremity of the patient. If a PRESup condition wasnot detected, a selected lower extremity characteristic ratio of about0.7 may be selected (568). This selected lower extremity characteristicratio may be used to calculate an indicated blood pressure value for thelower extremity. The indicated blood pressure value for the lowerextremity may in turn be used with an indicated blood pressure value forthe upper extremity (e.g., as arrived at using the characteristic ratiodetermined at step 532) to calculate an ABI value. It may be determined(566) if the calculated ABI value is greater than 0.75. If so, anindication (562) of PAD may be presented (e.g., without displaying thequantified value of the calculated ABI). If the patient's ABI value isdetermined (566) to be less than 0.75, the calculated ABI may bedisplayed (570) to a user.

FIG. 6 depicts one embodiment of a control module 200 where a display290 thereof can be seen. FIG. 6 also shows the connection of pneumatictubes 112, 122, 132, and 142 to the control module 200. Furthermore, aremovable storage interface 260 can be seen. In the embodiment depictedin FIG. 6, the removable storage interface 260 may comprises a USB portcapable of receiving a removable storage device (e.g., a flash drive).

The display 290 may also include a “START” button 602 to initiateperformance of a process (e.g. the process 400 and/or process 500 shownand described with respect to FIGS. 4 and 5, respectively) to obtain anoscillometric signal at each of one or more cuffs (e.g., as shown withreference to FIGS. 1 and 2). The display 290 may also include a displayof values for right ABI 604 and left ABI 606. Additionally, values forthe right upper extremity indicated blood pressure value 608 and leftupper extremity indicated blood pressure value 610 may be displayed, ifdetermined. Further still, the right lower extremity indicated bloodpressure value 616 and the left lower extremity indicated blood pressurevalue 608 may be displayed, if determined. Also, the control module 200may display additional patient information (e.g., left and rightpulmonary vascular resistance (PVR) values).

While various embodiments of the present invention have been describedin detail, further modifications and adaptations of the invention mayoccur to those skilled in the art. However, it is to be expresslyunderstood that such modifications and adaptations are within the spiritand scope of the present invention.

What is claimed is:
 1. A system operable to determine presence ofperipheral artery disease using an oscillometric blood pressure valueobtained at a lower extremity of a patient, said system comprising: afirst pressure applicator positionable at a location on the lowerextremity of a patient, said first pressure applicator beingcontrollable to apply a pressure to occlude blood flow in a portion ofthe lower extremity and to reduce the pressure applied thereby to permitblood flow to return in the portion of the lower extremity; a firstpressure transducer in operative communication with said first pressureapplicator to obtain a first oscillometric pressure signal from thelower extremity as pressure applied by the first pressure applicator tothe lower extremity is reduced; a second pressure applicatorpositionable at a location on an upper extremity of a patient, saidsecond pressure applicator being controllable to apply a pressure toocclude blood flow in a portion of the upper extremity and to reduce thepressure applied thereby to permit blood flow to return in the portionof the upper extremity; a second pressure transducer in operativecommunication with said second pressure applicator to obtain a secondoscillometric pressure signal from the upper extremity as pressureapplied by the second pressure applicator to the upper extremity isreduced; a processor in operative communication with said first pressuretransducer and with said second pressure transducer; a selection moduleexecutable by said processor, said selection module operating whenexecuted by said processor to compare the first oscillometric pressuresignal obtained by the first pressure transducer to the secondoscillometric pressure signal obtained by the second pressure transducerto characterize the patient into one of a first diagnostic class and asecond diagnostic class, said selection module also operating whenexecuted by said processor to select a lower extremity characteristicratio from a plurality of ratio values such that a first ratio value isselected from the plurality of ratio values if the patient ischaracterized by the selection module as being in the first diagnosticclass and a second ratio value is selected from the plurality of ratiovalues if the patient is characterized by the selection module as beingin the second diagnostic class; and a blood pressure determinationmodule executable by said processor, the blood pressure determinationmodule operating when executed by said processor (a) to detect a maximumamplitude of the first oscillometric pressure signal obtained by thefirst pressure transducer and (b) to multiply the detected maximumamplitude of the first oscillometric pressure signal by the selectedlower extremity characteristic ratio to provide an adjusted amplitudeassociated with the first oscillometric pressure signal to obtain anindicated blood pressure value in the lower extremity, the bloodpressure determination module also operating when executed by saidprocessor (x) to detect a maximum amplitude of the second oscillometricpressure signal obtained by the second pressure transducer and (y) tomultiply the detected maximum amplitude of the second oscillometricpressure signal by a selected upper extremity characteristic ratio toprovide an adjusted amplitude associated with the second oscillometricpressure signal to obtain an indicated blood pressure value in the upperextremity, the processor being operable to calculate a ratio between theindicated blood pressure value in the lower extremity obtained byoperation of the blood pressure determination module executed by saidprocessor and the indicated blood pressure value in the upper extremityobtained by operation of the blood pressure determination moduleexecuted by said processor to produce a blood pressure ratio forevaluating the presence of peripheral artery disease in the patient. 2.The system of claim 1, wherein at least one of the blood pressuredetermination module and the selection module comprises machine readablecode stored on a memory in operative communication with said processor,and wherein said processor is operable to execute said machine readablecode to execute said at least one of the blood pressure determinationmodule and the selection module.
 3. The system of claim 1, furthercomprising: a transform module executable by said processor to transformthe first oscillometric pressure signal into a frequency domainrepresentation of the first oscillometric pressure signal, and whereinthe blood pressure determination module operates when executed by saidprocessor to utilize the frequency domain representation of the firstoscillometric pressure signal in determining the maximum amplitude atthe fundamental frequency of the first oscillometric pressure signal. 4.The system of claim 1, wherein the upper extremity characteristic ratiois different than the selected lower extremity characteristic ratio. 5.The system of claim 1, wherein the indicated blood pressure values inthe upper and lower extremities comprise systolic pressure values. 6.The system of claim 1, wherein the location on the lower extremitycomprises an ankle of the patient, and the location on the upperextremity comprises an arm of the patient.
 7. The system of claim 6,wherein the blood pressure ratio comprises an ankle-brachial pressureindex (ABI).
 8. The system of claim 1, wherein said blood pressuredetermination module operates when executed by said processor todetermine said maximum amplitude of the first oscillometric pressuresignal within a window of interest of the first oscillometric pressuresignal.
 9. The system of claim 1, wherein the processor is in operativecommunication with the first pressure applicator and with the secondpressure applicator.
 10. A system operable to determine presence ofperipheral artery disease using an oscillometric blood pressure valueobtained at a lower extremity of a patient, said system comprising: afirst pressure applicator positionable at a location on the lowerextremity of a patient, said first pressure applicator beingcontrollable to apply a pressure to occlude blood flow in a portion ofthe lower extremity and to reduce the pressure applied thereby to permitblood flow to return in the portion of the lower extremity; a firstpressure transducer in operative communication with said first pressureapplicator to obtain a first oscillometric pressure signal from thelower extremity as pressure applied by the first pressure applicator tothe lower extremity is reduced; a second pressure applicatorpositionable at a location on an upper extremity of a patient, saidsecond pressure applicator being controllable to apply a pressure toocclude blood flow in a portion of the upper extremity and to reduce thepressure applied thereby to permit blood flow to return in the portionof the upper extremity; a second pressure transducer in operativecommunication with said second pressure applicator to obtain a secondoscillometric pressure signal from the upper extremity as pressureapplied by the second pressure applicator to the upper extremity isreduced; a processor in operative communication with said first pressuretransducer and with said second pressure transducer; a selection moduleexecutable by said processor, said selection module operating whenexecuted by said processor to compare the first oscillometric pressuresignal obtained by the first pressure transducer to a threshold value tocharacterize the patient into one of a first diagnostic class and asecond diagnostic class, said selection module also operating whenexecuted by said processor to select a lower extremity characteristicratio from a plurality of ratio values such that a first ratio value isselected from the plurality of ratio values if the patient ischaracterized by the selection module as being in the first diagnosticclass and a second ratio value is selected from the plurality of ratiovalues if the patient is characterized by the selection module as beingin the second diagnostic class; and a blood pressure determinationmodule executable by said processor, the blood pressure determinationmodule operating when executed by said processor (a) to detect a maximumamplitude of the first oscillometric pressure signal obtained by thefirst pressure transducer and (b) to multiply the detected maximumamplitude of the first oscillometric pressure signal by the selectedlower extremity characteristic ratio to provide an adjusted amplitudeassociated with the first oscillometric pressure signal to obtain anindicated blood pressure value in the lower extremity, the bloodpressure determination module also operating when executed by saidprocessor (x) to detect a maximum amplitude of the second oscillometricpressure signal obtained by the second pressure transducer and (y) tomultiply the detected maximum amplitude of the second oscillometricpressure signal by a selected upper extremity characteristic ratio toprovide an adjusted amplitude associated with the second oscillometricpressure signal to obtain an indicated blood pressure value in the upperextremity, the processor being operable to calculate a ratio between theindicated blood pressure value in the lower extremity obtained byoperation of the blood pressure determination module executed by saidprocessor and the indicated blood pressure value in the upper extremityobtained by operation of the blood pressure determination moduleexecuted by said processor to produce a blood pressure ratio forevaluating the presence of peripheral artery disease in the patient. 11.The system of claim 10, wherein at least one of the blood pressuredetermination module and the selection module comprises machine readablecode stored on a memory in operative communication with said processor,and wherein said processor is operable to execute said machine readablecode to execute said at least one of the blood pressure determinationmodule and the selection module.
 12. The system of claim 10, furthercomprising: a transform module executable by said processor to transformthe first oscillometric pressure signal into a frequency domainrepresentation of the first oscillometric pressure signal, and whereinthe blood pressure determination module operates when executed by saidprocessor to utilize the frequency domain representation of the firstoscillometric pressure signal in determining the maximum amplitude atthe fundamental frequency of the first oscillometric pressure signal.13. The system of claim 10, wherein the upper extremity characteristicratio is different than the selected lower extremity characteristicratio.
 14. The system of claim 10, wherein the indicated blood pressurevalues in the upper and lower extremities comprise systolic pressurevalues.
 15. The system of claim 10, wherein the location on the lowerextremity comprises an ankle of the patient, and the location on theupper extremity comprises an arm of the patient.
 16. The system of claim15, wherein the blood pressure ratio comprises an ankle-brachialpressure index (ABI).
 17. The system of claim 10, wherein said bloodpressure determination module operates when executed by said processorto determine said maximum amplitude of the first oscillometric pressuresignal within a window of interest of the first oscillometric pressuresignal.
 18. The system of claim 10, wherein the processor is inoperative communication with the first pressure applicator and with thesecond pressure applicator.